The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Pentax D FA 24-70mm F2.8 ED SDM WR and the Pentax DA 20-40mm F2.8-4 ED DC WR for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Pentax D FA 24-70mm F2.8 ED SDM WR is the longer of the two lenses at 110mm. The Pentax DA 20-40mm F2.8-4 ED DC WR with a length of 69mm, is 41mm shorter. Besides being longer, the Pentax D FA 24-70mm F2.8 ED SDM WR also has a larger diameter of 89mm compared to the Pentax DA 20-40mm F2.8-4 ED DC WR's 71mm diameter.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Pentax DA 20-40mm F2.8-4 ED DC WR weighs 283g, 64% (504g) lighter than the Pentax D FA 24-70mm F2.8 ED SDM WR's weight of 787g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Pentax KAF3 Mount for size comparison purposes.
Standard Lenses in Pentax KAF3 Mount for Size Comparison
Lens Mounts
Both the Pentax D FA 24-70mm F2.8 ED SDM WR and the Pentax DA 20-40mm F2.8-4 ED DC WR has the same Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with the Pentax KAF3 lenses are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III.
Focal Range
Pentax D FA 24-70mm F2.8 ED SDM WR has a focal range of 24-70mm and
2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
36 - 105mm.
On the other hand, the Pentax DA 20-40mm F2.8-4 ED DC WR has a focal range of 20-40mm and 2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 30-60mm when used on a APS-C / DX format camera.